Little Tony was 7 years old and was staying with his grandmother for a few days.
He'd been playing outside with the other kids for a while when he came into the house and asked her :

'Grandma, what'* that called when two people sleep in the same room and one is on top of the other?'
She was a little taken aback, but she decided to tell him the truth. 'It'* called sex, darling.'

Little Tony said, 'Oh, OK,' and went back outside to play with the other kids.

A few minutes later he came back in and said angrily,

'Grandma, it isn't called sex. ***It'* called Bunk Beds. And Jimmy'* mom wants to talk to you.'

Yes they do know everything. She just used her response last, so that is the most likely one she is going to remember.

Funny still however

Hahaha, I wasn't expecting that. My grandmother wouldn't ever say that to me, not that I would ever ask or anything.

haha yup Jimmy'* mom is probably preeeeety mad

For some reason I'm picturing the movie Stepbrothers.